DefinePK

Abstract

The effect of a single tensile overload held in certain period was investigated on the crack propagation behavior in front of the crack tip following the overload. The investigation was conducted by cycled the specimens under constant amplitude load with stress ratio to be zero, and after the crack had reached in certain length, the overload with and without combination of the hold period was subjected to specimens, respectively. The stress analysis in front of the crack tip was carried out by aid of software based on the finite element method. The result of the investigation shows that the hold period of the overload together with the magnitude of the overload affects the crack propagation behavior following the overload. The compressive residual stress developing in front of the crack tip after the overload causes the retardation of the propagation of the crack, and then the number of delay cycles increases. The development of the residual stress associates with the plastic strain of the element material in front of the crack tip caused by the overload, and the strain is increased by the hold period of the overload. However, the increasing of the plastic strain may lead to the crack tip to be blunt, and it reduces the effect of the compressive residual stress to the crack propagation behavior, thus, it decreases the number of delay cycles. In addition, because the hold period increases the plastic strain, upon unloading to zero load the plastic strain stretching to the overload direction is too high, and it reduces the magnitude of the compressive residual stress. Therefore, the hold period reduces the number of delay cycles after the overload.